Recently, human body communication has been suggested in which data communication using a human body as an interface is performed between a data communication device held by a user and a data communication device in communication with the user's data communication device. In such a data communication device employing the human body communication, the human body being a conductor is used as an antenna. The data communication device generally includes a plurality of electrodes exposed to the outside to make contact with a portion of the human body and a data communication unit for data transmission or reception.
In the data communication device based on the human body communication, it is required to secure sufficient contact between the electrodes and the human body. For that reason, there has been suggested a structure in which the electrodes are formed on the rear surface of a wrist watch or on the inner surface of a ring so that the electrodes are naturally brought into contact with the human body in a secure manner in the case where the data communication device is held by or equipped on the user.
For example, there is disclosed a data communication device, in which a data communication unit is incorporated into a wrist watch type package, and electrodes are arranged in the width direction of a band part of the wrist watch so as to be opposed to each other, thereby enabling users to make the most of the data communication device without needing to pay attention to the electrode arrangement (see Patent Document 1 for reference).
In addition, there is disclosed a data communication device, in which an electrode surface is formed on the entire inner surface of a band part, and a plurality of protrusions are formed in the longitudinal direction of the electrode surface, thereby making it easy to bring the electrode surface into contact with the human body and thus improving contact pressure therebetween (see Patent Document 2 for reference).
However, in the case where the human body communication is applied to a handheld information terminal such as a cellular phone or a PDA, if the user does not hold the handheld information terminal while paying attention to respective positions of the electrodes, signals from the handheld information terminal are not securely transmitted to the human body and thus making communication unstable, thereby disabling the communication.
Moreover, since it is likely that only protruding parts of the protrusions are brought into contact with the human body, it is difficult to secure a sufficient contact area between the electrode surface and the human body.
Patent Document 1: JP-A-2003-134009
Patent Document 2: JP-A-2004-064435